Underwater wellhead installation



F. 0. WEST UNDERWATER WELLHEAD INSTALLAT ION Aug. 19, 1969 2sheetsesheet l Filed March so, '1967 INVENTORZ FRANCIS G. WEST UnitedStates Patent 3,461,957 UNDERWATER WELLHEAD INSTALLATION Francis G.West, The Hague, Netherlands, assiguor to Shell Oil Company, New York,N.Y., a corporation of Delaware Filed Mar. 30, 1967, Ser. No. 627,126Claims priority, application Great Britain, May 27, 1966,

27/66 Int. Cl. E21b 33/035, 43/01 US. Cl. 166.5 3 Claims ABSTRACT OF THEDISCLOSURE The present invention relates to an underwater wellheadinstallation mounted on a tube cemented to a formation underlying thebottom of a body of water.

According to recent practice, the wellhead installations of wells whichhave been drilled in formations underlying a body of water are mountedat some distance below the surface of the water so as to reducenavigation hazards. These wellhead installations may be remotecontrolledvia electric or hydraulic conduits passing from a suitable controlcenter to the installations, or controlled manually by divers operatingeither freely or by means of diving bells.

Numerous methods are known for drilling such wells through formationsunderlying a body of water, the wells being completed by means ofwellhead installations which are below the surface of the water butabove the bottom of the body of water. Control of the operations whichhave to be performed by the wellhead installations during the productionof oil or gas from the wells on which they are mounted is preferablycarried out by remote control. Servicing operations on the wellhead oreven in the well itself may be carried out by a diver, provided that thedepth at which such an installation is located does not exceed the depthat which a diver can work. To service a wellhead installation manuallybut without the use of divers, it has already been proposed to installthe wellhead installation in a water-tight housing which is arrangedbelow the surface of the sea. Access can be gained to such housing bymeans of a caisson which at its lower end is connected to the housing ina liquidtight manner, and at its upper end communications with the spaceabove the water. By pumping the water out of the caisson, the hatchgiving access to the housing can be opened, and a workman can enter viathe caisson. The housing can be located fully above the formationunderlying the body of water, or it may extend for the greater part intothat formation.

Although the application of the above-mentioned housing used forprotecting a submerged wellhead installation will certainly reducenavigation hazards as long as the housing is located at a depth greaterthan the maximum draught of the ships passing through the area where thehousing is located, such housing is, however, liable to damage when usedin an area where fishing boats are operating. An object of the presentinvention is to provide a means suitable for protecting an underwaterwellhead installation against damage by boats.

A further object of the present invention is to provide Patented Aug.19., 1969 "ice a means for protecting an underwater wellheadinstallation, said means being so designed that no damage will be doneto fishing nets, tackle, etc., which are being passed through the waterby fishing boats, sometimes very close to the sea bed (e.-g., trawlfishing).

According to the invention, an underwater wellhead installation mountedon a tube cemented to a formation underlying the bottom of a body ofwater, is located in a cellar structure which has its upper wallsubstantially flush with the bottom of the body of water.

The expression substantially flush with the bottom of the body of water,or in other words substantially flush with the top of the formationunderlying the body of water, means throughout the present specificationeither in the plane forming the lower boundary of the body of water, orin a plane other than that plane, provided that this second plane has agently curving slope, intersects the lower boundary of the body of wateralong a closed line, and shows at its intersection with the first planean angle which is greater than with respect to this lower boundary.

Preferably, the entry to the cellar is formed by an opening in the upperwall or roof portion of this cellar structure, which opening is coveredby a removable lid. If desired, the whole roof portion of the cellarstructure may be formed by the removable lid.

In the following, three embodiments of the invention will be describedby way of example.

FIGURE 1 is a cross sectional view of a metal cellar structure locatedbelow the bed of the sea, which cellar structure is provided with acover closing the entry to the cellar, the top of the cover being in thesame plane as the sea bed;

FIGURE 2 is a cross sectional view of an alternative of the constructionaccording to FIGURE 1; and

FIGURE 3 is a cross sectional view of another alternative constructionshowing a concrete cellar structure located in the bed of the sea, whichcellar has a slightly curved roof portion.

The cellar 1, as shown in FIGURE 1 of the drawing, is located in theformation 2 which lies below the sea 3, the bed or floor 4 forming theboundary between the formation 2 and the sea 3. The top surface of thesea is indicated by line 5. The depth of the sea or body of water may beof any magnitude.

The cellar 1 is bounded laterally by a cylindrical side wall 6 made ofmetal, and at its bottom end by the circular metal plate 7, which isconnected to the wall 6, e.g., by welding. An opening is provided in theplate 7, through which opening the conductor 8 is arranged. Conductor 8and plate 7 are connected together, e.g., by welding.

The top of the cellar 1 is closed by a cover or lid 9 which has adiameter greater than the diameter of the wall 6 and is supported by aring member 10 welded to the outer face of the wall 6.

The cover '9 is provided with at least one depression 11 in which ameans 12 (such as a bar) is arranged, which means is suitable for beingconnected to a hook or the like for lifting the cover from the side wall6 of the cellar 1.

In the embodiment as shown in FIGURE 1, no particular sealing means arearranged between the cover 9 and the side wall 6 (or the ring 10), sincethe Way in which the cover 9 is supported by the ring member 10 ensuresthat the amount of foreign matter which can enter in this way into thecellar 1 will be extremely small and will in no way hamper theoperations to be carried out within the cellar 1. If desired, however, asimple sealing ring may be arranged to close the entry to the cellar toforeign matter, such as sand or silt.

Through the conductor 8, a casing 13 is arranged. Where this casingprotrudes from the lower end of the conductor 8, the greater part of itis cemented to the formation 2, and if necessary to any other formation(not shown) below this formation 2. On top of the casing 13, a spoolpiece 14 is mounted, which spool piece carries a schematically indicatedwellhead 15. The production tubing (not shown) arranged within thecasing 13 communicates in a known manner with the wellhead.15, and withthe flowline 16 connected via coupling 17 with the Wellhead 15. Sincethe present invention is not directed to any detail of the wellhead, andin fact any type of wellhead may be used, no details are given in FIGURE1 of the drawing.

A ladder 18 has been mounted on the inner face of the well 6 to enablethe diver or divers to descend into the cellar 1 once the cover 9 hasbeen lifted therefrom.

Although in the design of the cellar structure as shown in FIGURE 1 theflow conduit 16 passes through the side wall 6 of the structure, thisflowline may if desired in an alternative arrangement, pass through thebottom plate 7.

The sequence of steps to be carried out for installing the wellheadinstallation according to the invention will now be described in detail.

The borehole, in which the well is to be arranged, is drilled by means(not shown) such as by rotary drilling equipment which is supported by afloating platform or by a platform supported on legs on the sea bed 4.The first tubing to be placed in the drilled borehole is formed by theconductor 8. To this end, the conductor 8 is connected to the cellarstructure consisting of the bottom plate 7 and the side wall 6. Theassembly thus formed may be lowered from the drilling platform into ahole which has been pre-drilled into the formation 2. If conditions ofthe formation 2 so allow, the assembly consisting of the side wall 6,the bottom plate 7 and the casing 8 is spudded in by water jets issuingout of conduits (not shown) which are connected to the assembly and havetheir outlets located at or near the lower end of the casing 8 and nearthe bottom plate 7. Suitable pumps (not shown) are arranged on thedrilling platform for supplying Water under pressure to these conduits.

While being supported in the position as shown in FIGURE 1 of thedrawing, the assembly is then cemented to the formation 2 by usingcementing equipment which is normally used for cementing conductors inthe formation. The cement is passed in a downward direction through theconductor 8 (or a conduit arranged in the conductor 8) to the lower endthereof, and returns in an upward direction along the outer side of theconductor 8 and the outer face of the plate 7 and the side wall 6. Afterthe cement has hardened, a drill bit with drill string is passed throughthe cellar 1 and the interior of the conductor 8 to drill a hole throughthe formation 2. Any type of equipment suitable for submerged drillingand completion of wells may be used for the purpose. Thus, guide lines(not shown) extending between the cellar 1 and the drilling platform maybe applied for guiding the required equipment to the entrance of theconductor 8. To this end, suitable coupling means (not shown) may bearranged on the upper side of the bottom plate 7 for connecting thelower ends of the guide lines thereto.

After a sufiicient depth has been reached by the borehole, a casing 13is introduced into the hole, which casing is cemented to the formationsunderlying the formation 2. If necessary, other casings (not shown) maybe placed.

The well is completed by the spool 14 and the wellhead 15, from which aproduction tubing (not shown) is suspended into the well. The upper endof this production tubing is connected via coupling 17 to the conduit 16which has been layed by divers below the sea bed 4, and which passesthrough the side wall 6.

The ladder 18 may be placed in the cellar structure before lowering thelatter into the sea, or after the cellar structure is in place.

After the Well has been completed, the entrance to th cellar 1 is closedby the cover 9. If required, this cover can be bolted to the side wall 6or even locked thereto to prevent unauthorized entry to the cellar 1.The handling of the cover 9 can be effected from the drilling platformby means of a crane, or by divers using gasfilled bags or other buoyantlifting devices tied to the cover.

The interior of the cellar 1 remains filled with sea water. If desired,corrosion inhibiting means may be placed in the cellar 1.

Alternatively, the cellar may be placed first, by other constructionequipment, and form part of the well location to which and over whichthe drilling outfit is brought up.

It will be clear that the invention is not restricted to the manner asshown in FIGURE 1 for supporting the cover 9. In an alternative manner,the cover 9 may have a vertical flange of a diameter smaller than theinner diameter of the Wall 6 and be supported by a ring member attachedto the inner face of the wall 6 as shown in FIGURE 2. In addition, thecover may be provided with a socket 19 (see FIGURE 2) cooperating with aspigot 19" attached to the wellhead 15. If desired, the cover 9 may bemade of reinforced concrete.

In the embodiment of the invention as shown in FIG- URE 3, the materialused for the construction of the cellar walls is reinforced concreteinstead of metal. This type of cellar structure is especially useful inareas in which the shape of the sea bed is liable to undergo changes dueto currents or tides.

The cellar 20 in FIGURE 3 comprises an integral concrete structureconsisting of the side wall 21, the bottom 22 and the curved roofportion 23. The roof portion 23 is larger than the cellar 20 so that itoverhangs the cellar and includes an opening which in the position asshown is closed by a cover 24. The periphery of the roof portion 13 ispreferably partially buried in the sea bed or floor 25.

Although the cross-section of the roof portion 23 is part of a sphere inthe embodiment as shown, it will be clear that any other curved shapemay be used. The angle A between the sea bed or floor 25 and the tangentT-T passing through the vertical axis of symmetry S-S and the placewhere the outer plane of the roof portion 23 and the sea bed 25intersected is greater than The bottom 22 of the cellar 20 is providedwith an opening through which a conductor tubing 26 which is cemented tothe formation 27 underlying the sea bed 25 passes in a liquid-tightmanner. The upper end of the conductor 26 is not flush with the bottom22 of the cellar as in the embodiment shown in FIGURE 1, but extends upto a level between the bottom and the to of the cellar 20.

Supported by the conductor 26 and/or by the wall(s) of the cellar 20, aworking-platform 28 is arranged at some distance above the bottom 22,thereby creating a space in the lower part of the cellar 20 suitable forthe storage of a liquid 35 having a specific gravity greater than thespecific gravity of the sea water. 1

A wellhead 29 is mounted on top of the casing 30 and communicates with aconduit 31 which passes through the side wall 21 of the cellar 20 andruns below the sea bed 25 to a place where the product produced from thewell can be used or stored.

Also mounted in the cellar 20 is a pump system comprising a suctionconduit 32, a pump 33 and a pressure conduit 34, the outlet of whichcommunicates with the tubing system arranged Within the well. By fillingthe lower part of the cellar 20 with glycol a continuous or interruptedinjection of glycol by means of this pump system will prevent hydrateforming if the well produces gas. The energy for activating the pump maybe obtained from the gas flowing from the well. If desired, a liquidother than glycol may be stored in the lower span of the cellar 20.

The liquid may be supplied to the cellar 20 by a small pipeline from acontrol center or by a hose from a supply-boat on the sea surface.

Instead of using an open space for the storage of liquid as indicated inFIGURE 3, a fully formed tank may be situated in the lower part of thecellar 20, thereby creating a space suitable for storing liquids (havinga specific gravity either lower or higher than the specific gravity ofthe sea water) to be used for injection into the well (e.g., aninhibitor or an anti-hydrate formation liquid). Such liquid is thenentirely separated from the sea water, and can be pumped to the desiredlocation by a pump system suitable for the purpose. The liquid may bereplenished in the same manner as described above with reference toFIGURE 3.

The advantage of the curved roof portion 23 of the cellar 20 will beapparent from FIGURE 3. Even when the material from the upper layer ofthe formation 27 is displaced, thereby forming hollows in the localityof the cellar structure, this structure does not show any point ontowhich objects such as anchors or trawl nets being dragged over the seabed can hook. Damage of the cellar structure as well as anchors or trawlnets is thus prevented.

The concrete cellar structure is preferably placed on fl1e desiredlocation before the drilling operations start. The conductor tubing isthen placed in position in a drilled hole by lowering it through theopening provided in the bottom 22. If desired, any other manners ofplacing the conductor 26 may be applied. The conductor is then cementedto the formation 27, and if necessary, the opening left between theconductor tubing 26 and the bottom 22 may be closed off by divers usingsuitable sealing material. The operations for placing the casing 30; thewellhead 29 and the flowline 31 take place in a manner similar to thatdescribed with reference to FIGURE 1.

It will be clear that the invention is not restricted to cellarstructures with curved roof portions 23 extending outside the areaenclosed by the side wall 21 as shown in FIGURE 3. If desired, the areaenclosed by this wall 21 may be enlarged, and the wall 21 may beconnected to the roof portion 23 near the outer edge thereof.

The axis of the well need not necessarily coincide with the axis of thecellar structure as shown in FIGURES 1, 2 and 3. However, the cover orlid closing the opening provided in the roof portion of the cellar mustbe above the well entry. This cover or lid may be of any shape, but ispreferably of circular form.

The interior dimensions of the cellar have to be sufiicient to allow aworking space for at least one diver. Preferably, the diameter of thecellar, provided with a cylindrical side wall is used, is about 3 feet.A height of about 3% feet will be sufiicient as working height. If

6 liquid is stored (see FIGURE 3), a greater height of the cellar willbe required.

When using a diving bell for servicing the Well, it is preferred toarrange means within the cellar or on the roof portion thereof suitablefor centering the diving bell on the cellar structure.

I claim as my invention:

1. An underwater wellhead installation comprising:

a substantially closed cellar structure mounted substantially flush withthe floor of a body of water, said cellar including an enclosed verticalwall, a bottom having at least one opening and a top closure;

a well casing conductor extending through said opening in said bottomand extending downwardly into a formation underlying the floor of saidbody of water;

said top closure having a generally dome shaped roof secured to andoverhanging said vertical wall;

said roof being formed with an access opening in communication with theinterior of said cellar structure;

a removable cover carried by said roof to close said access opening;

said cellar structure forming an enclosure for a wellhead positionableon the well casing extending through said conductor into a formationunderlying said floor of said body of water; and,

wherein the lower portion of said cellar structure comprises a liquidstorage chamber.

2. An underwater wellhead installation as defined in claim 1 including:

pump means mounted within said cellar structure and having an inlet incommunication with said liquid storage area and an outlet incommunication with said well.

3. An underwater wellhead installation as defined in claim 2 including:

a working platform carried by said cellar structure and arranged abovesaid liquid storage chamber.

References Cited UNITED STATES PATENTS 2,729,966 1/ 1956 Lutteke 52169 X2,747,840 5/1956 Miles -9 2,756,021 7/1956 Townsend et al 175-9 X2,854,215 9/1958 Cox et al 166-.5 3,063,500 11/ 1962 Logan 166-.53,202,218 9/ 1965 Watts et al 166.5 3,247,672 4/ 1966 Johnson 166.5

CHARLES E. OCONNELL, Primary Examiner R. E. FAVREAU, Assistant Examiner

